1. Field of the Invention
The present invention relates to a magnetic disc drive system which prevents the damage of data recorded on such a magnetic disc as a floppy disc by an adsorbent phenomenon of a magnetic head when the recording and reproducing operations of the head are stopped.
2. Description of the Prior Art
Recently, a floppy disc drive system (hereinafter, which is referred to merely as the FDD) has been widely employed in a backup memory of a telephone exchange system, a word processor and so on. In the conventional FDD, a magnetic head is stopped at its initial stage at the outermost periphery of a floppy disc (hereinafter, which will be referred to merely as the disc) and during stoppage of the recording or reproducing operation, the magnetic head remains on a track on the disc at the corresponding position. For this reason, the conventional FDD has had such a problem that when the magnetic head and the disc are left under high temperature and high humidity conditions for a certain period of time, the magnetic head tends to adhere to the disc, that is, a so-called adsorbent or adhesive phenomenon tends to take place, which results undesirably in that information stored on the disc is destroyed or a rotary drive device cannot rotate the disc.
Most FDDs, which use a disc having a diameter of, for example, 3.5 inches, are not equipped with such a head loading mechanism as loads and unloads the disc with the magnetic head (connects and disconnect the magnetic head to and from the disc) for the purpose of miniaturization of the FDD. For this reason, in the 3.5-inch FDD, when the recording or reproducing operation has been ended, the magnetic head remains stopped at the then track position in a contact relation with the disc to ready for the next operation, which further increases the possibility of occurrence of the adsorbent phenomenon.
Especially in a PBX (private branch exchange) or a key telephone system which uses the aforementioned FDD as a memory backup device in case of power failure, the FDD is used to store exchange programs and customer data (abbreviated dialling numbers, ID codes and so on to be registered by users). In this respect, the FDD is driven only when it is necessary to rewrite the customer data and the disc is usually left in its loaded condition, i.e., loaded in the FDD for a long period of time, which leads to a much increased danger of occurrence of the disc adsorbent phenomenon.
The mechanism of the adsorbent phenomenon is not clear yet, but it is generally considered that under high temperature and high humidity conditions, surface active agent coated on the surface of a disc increases its fluidity and starts to flow into a contact area between the disc and a magnetic head by the capillary action, whereby the magnetic head adheres to the disc. And when the adsorbent or adhesive force exceeds a starting torque of a disc driving motor, the disc motor cannot rotably drive the disc or the disc is subjected to an unreasonable force on its surface on which data are recorded, leading to the destruction of the data.